Non-integral frequency dividers are known in the art. Non-integral frequency dividers divide a reference frequency according to a non-integral division ratio to produce a desired output frequency. Unfortunately, there are several drawbacks associated with existing non-integral frequency dividers. For example, existing non-integral frequency dividers are typically restricted in application and/or introduce undesirable complexity which results in increased cost.
A particular example of a known non-integral frequency divider includes a phased locked loop used with a pair of integral dividers to synthesize the desired frequency. However, the components in a phase locked loop are typically large, difficult to integrate into a digital integrated circuit, and can be mechanically delicate, therefore affecting the reliability, cost and application of such a frequency divider. In addition, the phase locked loop may exhibit an undesirable start up or settling time, which must be taken into account during design.
Other examples of non-integral frequency dividers are described in U.S. Pat. Nos. 3,818,354 to Tomisawa et al. and 4,555,793 to Benamy. The '354 patent describes a pulse frequency dividing circuit which utilizes ring counters formed with shift registers. The use of ring counters, however, typically requires large division ratios and results in a frequency dividing circuit with very limited application. Moreover, the frequency dividing circuit using ring counters is efficient as far as component cost only for select division ratios. The efficiency of such a frequency dividing circuit for other division ratios decreases substantially as will be appreciated by those familiar in the art. The '793 patent describes a non-integer frequency division apparatus which employs a shift register. However, it will be appreciated that the precision of such a frequency dividing circuit is limited and increases approximately only linearly with the size of the shift register.
In view of the aforementioned shortcomings associated with existing non-integral frequency dividers, there is a strong need in the art for a non-integral frequency divider which can perform high precision division for an arbitrary division ratio. Furthermore, there is a strong need for such a frequency divider which employs only simple logic circuitry and is cost efficient. In addition, there is a strong need in the art for a non-integral frequency divider which is capable of small division ratios and can be used in a large range of applications.